1. Field of the Invention
The present invention relates to the use of light filters in optical measuring systems and, more particularly, the operation and control of multiple position filter changing mechanisms in such systems.
2. Background of the Invention
Many optical measuring systems including but not limited to photometers, spectrophotometers, fluorometers, and the like, are adapted to perform optical measurements with various optical filters positioned in the optical measuring path. Depending upon the nature of the sample to be analyzed, the type of instrument to be employed, and the operating conditions to be satisfied, different filters or combination of filters are required to be positioned in the optical path. In order to simplify the filter positioning operation, various multiple position filter changing mechanisms have been developed which are controllable to automatically select the required filters. One common and mechanically simple form of filter changing mechanism is a filter wheel or disc supporting a plurality of filters or filter combinations at spaced circumferential positions around the disc. The disc is rotated or otherwise advanced to position various ones of the filters in the optical path sequentially.
The control of such filter changing mechanisms has been effected in several basic ways. In one approach the filter mechanism is connected to and driven by mechanical linkages which slave the filter mechanism to the mechanical state of other system components. In another approach, a separate position sensing device monitors the position of the filter mechanism and sends filter mechanism position information via a closed loop feedback control network to a filter mechanism controller. While the above approaches function satisfactorily to control filter mechanism positioning, they require additional control elements and logic and generally are less versatile and more costly than desired.